Atrial fibrillation is a common sustained cardiac arrhythmia and a major cause of stroke. This condition is perpetuated by reentrant wavelets propagating in an abnormal atrial-tissue substrate. Various approaches have been developed to interrupt wavelets, including surgical or catheter-mediated atriotomy.
A common procedure involves ablating a lesion to interrupt the wavelets using one or more electrodes mounted on the distal end of a generally-straight catheter. This procedure works well, for example, when ablating a line of block in the atria. However, for tubular regions in or around the heart, this procedure is less effective. For example, when the line of block is to be made about a circumference of the tubular region, it is difficult to manipulate and control the distal end of a straight catheter so that it effectively ablates about the circumference.
Catheters with circular ablation assemblies are known. For example, a particularly useful catheter is disclosed in U.S. Pub. No. 2003/0195508 (Scheib), the disclosure of which is hereby incorporated by reference. This catheter comprises a catheter body having at its distal end an ablation assembly with a preformed generally circular curve with an outer surface and being generally transverse to the axis of the catheter body. In this arrangement, the catheter has at least a portion of the outer circumference of the generally circular curve in contact with the inner circumference of a tubular region in or near the patient's heart, e.g., a pulmonary vein. However, one drawback with catheters of this type may be the relatively fixed size or circumference of the circular ablation assembly, which may not match the circumference of the tubular region undergoing treatment.
Ablation catheters with expandable assemblies are also known. Such a catheter is disclosed in U.S. Pat. No. 6,416,511 (Lesh), wherein the circumferential ablation element includes an expandable member with a working length that is adjustable from a radially collapsed position to a radially expanded position. This catheter employs an equatorial band that circumscribes the outer surface of the working length and is adapted to ablate tissue adjacent thereto when actuated by an ablation actuator. However, like most catheters with expandable members, the expandable member is a balloon structure that is inflated with a pressurized fluid source. In addition to certain complexities associated with use of a pressurized fluid source, inflation of the balloon undesirably restricts blood flow. Added complications may also arise when a balloon is forced to seat in the ostium near the treatment region, such as a pulmonary vein.
Moreover, the use of an ultrasound transducer, which often accompanies a balloon for purposes of locating or visualizing the assembly at the ostium has also caused complications because of the size of the transducer. As a relatively bulky and cumbersome accessory, the transducer can be difficult to maneuver and hamper the positioning of the balloon/transducer combination.
Also known is a basket catheter having a basket-shaped electrode array with a mechanism for expanding and retracting the electrode array, as described in U.S. application Ser. No. 10/017,564, the content of which is hereby incorporated by reference. The basket assembly has a plurality of spines connected at their proximal and distal ends to an expander that is movable longitudinally to expand and contract the basket-shaped electrode. While this assembly can accomplish circumferential ablation, it may be better suited for mapping and other diagnostic procedures in the chamber areas of the heart. Furthermore, wire spines of basket assemblies can in certain circumstances move or shift relative to each other, rendering the structure of the basket assemblies less stable than desirable.
Accordingly, a need exists for an improved catheter that is particularly useful for circumferential ablation in or near the ostium of tubular regions of the heart, especially in regions of varying or nonuniform circumference, and/or noncircular cross-sections. It is desirable that the ablation assembly has a sufficiently stable framework and that it minimizes disturbance to blood flow in the region. It is further desired that the ablation assembly be detectable by means other than through the use of ultrasound transducer which requires the application of a saline field.